The retrovirus designated “human immunodeficiency virus” or “HIV” is the etiological agent of a complex disease that progressively destroys the immune system. This disease is known as acquired immune deficiency syndrome or AIDS. As at Dec. 2005 an estimated 40 million people are living with HIV world wide and over 3 million deaths are occurring annually.
A feature of retrovirus replication includes the reverse transcription of the viral genome into proviral DNA and its integration into the host cell genome. These steps are required for HIV replication and are mediated by the virus encoded enzymes, reverse transcriptase and integrase respectively.
HIV infection follows a path of the virus particle binding to cell surface receptors and co-receptors resulting in fusion of the virus particle with the cell. The contents of the virus are released into the cytoplasm where reverse transcription of the HIV genome occurs. Through a series of steps a double stranded proviral DNA copy is produced. The proviral DNA is transported to the nucleus in a complex known as the pre integration complex (PIC) which contains integrase and other viral and possibly cellular proteins. Once inside the nucleus the proviral DNA is integrated into the host cell genome via the action of integrase. Once integrated, transcription and translation of the viral genome can occur resulting in the production of viral proteins and a new viral RNA genome. These proteins and genome assemble at the cell surface and, depending on cell type, possibly other intracellular membranous compartments. Assembled particles then bud out from the cell and during, or soon after, this process mature into infectious HIV particles through the action of the viral protease.
The integration of the proviral genome into the host cell genome requires the action of an integrase which carries out this process in at least three steps, possibly four. The first step involves the assembly of the viral genome into a stable nucleoprotein complex, secondly, processing of two nucleotides from the 3′ termini of the genome to give staggered ends with free 3′ OH residues and thirdly the transfer of these ends into the host cell genome. The final step involves the gap filling and repair of the insertion site in the host genome. There is still some conjecture over whether the integrase performs this final step or whether it is carried out by cellular repair enzymes.
Currently HIV infection can be treated with a number of inhibitors on the market which target reverse transcriptase, protease or entry into the cell. Treatment of HIV infection with these, or a combination of these, drugs is known to be an effective treatment for AIDS and similar diseases. Shortcomings with the current inhibitors include the rapid emergence and increase incidence of resistance and numerous side effects and hence there is a need for new classes of inhibitors targeting proteins such as integrase.